Importance of periphytic biofilms for carbon cycling in paddy fields: A review

Paddy fields play an important role in global carbon (C) cycling and are an important source of methane (CH4) emissions. Insights into the processes influencing the dynamics of soil organic C (SOC) in paddy fields are essential for maintaining global soil C stocks and mitigating climate change. Periphytic biofilms composed of microalgae, bacteria, and other microorganisms are ubiquitous in paddy fields, where they directly mediate the transfer of elements at the soil-water interface. However, their contributions to C turnover and exchange have been largely neglected. Periphytic biofilms affect and participate in soil C dynamics by altering both abiotic (e.g., pH and redox potential) and biotic conditions (e.g., microbial community composition and metabolism). This review summarizes the contributions of periphytic biofilms to soil C cycling processes, including carbon dioxide fixation, SOC mineralization, and CH4 emissions. Future research should be focused on: i) the mechanisms underlying periphytic biofilm-induced C fixation and turnover and ii) quantifying the contributions of periphytic biofilms to soil C uptake, stabilization, and sequestration in paddy fields.